1. Field of the Invention
The present invention relates to an exhaust device for discharging air in an image forming apparatus to an outside of the image forming apparatus and an image forming apparatus provided with the same, and to a computer readable recording medium on which a control program for the exhaust device is recorded.
2. Description of the Related Art
In electrophotographic image forming apparatuses such as copiers, printers, and facsimiles, a photoreceptor provided with a photosensitive layer including a photoconductive material on a surface thereof as an image bearing member is used, electric charges are applied onto the surface of the photoreceptor to uniformly charge the surface by a charging device, an electrostatic latent image corresponding to image information by various image forming processes is formed, the electrostatic latent image is developed into a visible image by a developer including a toner supplied from a development device, the visible image is transferred onto a recording medium such as paper, it is heated and pressurized by a fixing roller to fix it to the recording material, thereby forming an image on the recording material.
There is a case where a brush-shaped or roller-shaped contact-type device used in contact with a target is used as a charging device and a transfer device, but the roller-shaped or brush-shaped charging device and transfer device come into contact with a photoreceptor, an intermediate transfer belt, or similar to cause abrasion deterioration of the photoreceptor or the intermediate transfer belt. For this reason, recently, there are many cases where the contact-type charging device, transfer device, and similar are employed in an image forming apparatus with a relatively low printing speed, and a corona charging device (of scorotron charger type, etc.) is employed in an image forming apparatus with a high printing speed.
The corona charging device is suitable for image forming apparatus with the high printing speed, but it is difficult to avoid generating a discharge product such as ozone (O3) and nitrogen oxide (NOx) in the device. Specifically, nitrogen molecules (N2) in the air are dissociated into nitrogen elements (N) by energy based on discharge of electrons emitted from the corona charging device, and the nitrogen elements are bonded to oxygen molecules (O2), thereby generating nitrogen oxides (nitrogen dioxides: NO2). Similarly, oxygen molecules (O2) in the air are dissociated into oxygen elements (O), and the oxygen elements are bonded to oxygen molecules (O2), thereby generating ozone (O3).
When the ozone with high concentration is generated in the image forming apparatus as described above, the photoreceptor deteriorates through intensive oxidization of the ozone, and deterioration of image quality of printing (such as pinhole) may occur. When the nitrogen oxides are generated in the image forming apparatus, products based on the nitrogen oxides are attached onto the surface of the photoreceptor to diffuse the electric charges of the photoreceptor, and deterioration of image quality of printing (such as pinhole) may occur.
To solve such problems, the image forming apparatus is provided with an exhaust device that compulsorily discharges the ozone and discharge products in the apparatus with the air out the apparatus. In addition, the exhaust device may be provided therein with an ozone decomposition filter to lower the concentration of the ozone discharged to the outside of the image forming apparatus.
Japanese Unexamined Patent Publication JP-A 5-269340 (1993) discloses an exhaust device in which a continuation drive time at the time of continuously driving an exhaust unit from the point in time when ending a printing operation in an image forming apparatus is controlled according to the number of printing copies of one job. As described in JP-A 5-269340, when the continuation drive time of the exhaust unit is controlled according to the number of printing copies of one job, it is possible to discharge the ozone and discharge products in the image forming apparatus, concentrations of which become high substantially in proportion to the number of printing copies, out of the apparatus. Japanese Unexamined Patent Publication JP-A 2004-325994 discloses an exhaust device in which a drive time of an exhaust unit discharging the ozone in an image forming apparatus out of the apparatus is controlled according to use circumstance conditions (such as humidity condition).
However, a deterioration degree of image quality of printing such as pinhole caused by the ozone and discharge products in the image forming apparatus are varied according to the number of printing copies of one job and the use circumstance conditions, and is varied depending on a deterioration degree of a photoreceptor. For this reason, in the exhaust devices disclosed in JP-A 5-269340 and JP-A 2004-325994 in which the continuation drive time of the exhaust unit is controlled according to only the number of printing copies of one job or the use circumstance conditions, the deterioration of image quality of printing caused by the ozone and discharge products cannot be sufficiently suppressed. On the contrary, in order to sufficiently suppress the deterioration of image quality of printing, it is necessary to start to drive the exhaust unit with a drive output value set high to obtain high exhaust capability, and unnecessary power consumption cannot be suppressed.